Co-Existence of Optical Supervisory Channel-Enabled High-Power Classical Signals and Quantum Key Distribution Over Field-Deployed Fiber Networks

The co-existence of quantum key distribution (QKD) signals with classical optical signals in a single fiber enables substantial fiber resource savings and reduces the deployment costs of QKD networks. However, conventional approaches to mitigate the impact of strong classical signals on QKD performance typically involve reducing classical optical power, which inherently conflicts with standard optical communication network specifications and impedes the widespread adoption of QKD networks. In this work, we explore the feasibility of integrating QKD networks with high-capacity classical optical networks without significant modifications to existing infrastructure and validate wavelength allocation strategies for their co-existence in field-deployed shared fibers. Notably, we demonstrate co- propagation of QKD with high-power classical signals (21.75 dBm total launch power) over 81 km of commercial backbone fiber, covering 90% of China Telecom's inter-site links. Leveraging a 400 Gbps optical transport network (OTN) system, we first, to the best of our knowledge, achieve a classical optical capacity of 15.7 Tbps. Additionally, we introduce single-fiber optical supervisory channel (OSC) configurations in quantum-classical co-existence experiments for the first time, further validating the feasibility of integrating QKD networks with classical networks requiring high-precision clock synchronization. The system achieves secure key rates (SKRs) of 2.2 kbps and 1.35 kbps under two-fiber and single-fiber OSC configurations, respectively. This study marks a significant step towards the practical deployment and maturity of QKD networks.